Tungalag Dong

Interactions between an anticancer drug and polymeric micelles based on biodegradable polyesters.

Interactions between the anticancer drug quercetin and biodegradable polyesters within micelles were investigated by DSC, WAXD, and UV analyses. For micelles based on poly(ethylene glycol) methyl ether-block-poly(epsilon-caprolactone) (MPEG-PCL), DSC analysis indicated that the interactions were between the hydrophobic core and the drug within the micelle. For micelles based on poly(ethylene glycol) methyl ether-block-poly(L-lactide) (MPEG-PLLA), the interactions were between the hydrophobic core and the drug and between hydrophilic segments and the drug. WAXD results indicated that no crystalline phase of the drug was found in either of the micelle types. Based on the DSC and WAXD results, two probable micelle structures were proposed. The UV spectra revealed the presence of hydrogen bonding as the main interaction between the drug and the polyesters. In vitro studies demonstrated that quercetin release from micelles was sustained and was affected by the polymer-drug interaction.

Conformational and microstructural characteristics of poly(L-lactide) during glass transition and physical aging.

The glass transition and physical aging processes of poly(L-lactide) (PLLA) were studied by variable-temperature Fourier transform infrared (FTIR) spectroscopy and (13)C solid-state NMR spectroscopy. The glass transition temperature (T(g)) of PLLA can be well determined from the temperature-dependent FTIR intensity. Nearby T(g), a distinct change in the slope of spectral intensity versus temperature plot is detected. FTIR results suggest that the energy-favorable gauche-trans (gt) conformers rearrange into the less energy-favorable gauche-gauche (gg) counterparts with heating over the glass transition region, which becomes more distinct at temperature above T(g). Besides, the 1267 cm(-1) band, which shows different trends of variation from the other bands upon heating, was assigned to be more sensitive to the nu(as)(C-O-C)+delta(CH) vibration mode of the less energy-favorable gg conformers in PLLA. By comparing the FTIR spectra of the aged and deaged PLLA, it was demonstrated that the rearrangement from the high- to low-energy conformers, i.e., gg to gt, occurs with physical aging. (13)C spin-lattice relaxation measurements indicate that the relaxation rate distribution broadens with aging, which agrees with the previous suggestion that the locally ordered domains are formed during physical aging. Because of the larger variation in the conformational state and microstructure, the FTIR intensities vary much more abruptly for the aged sample with heating to nearby T(g).

Alternating poly(lactic acid)/poly(ethylene-co-butylene) supramolecular multiblock copolymers with tunable shape memory and self-healing properties

Alternating supramolecular multiblock copolymers with hard poly(lactic acid) (PLA) and soft poly(ethylene-co-butylene) (PEB) segments were prepared by terminal functionalization of PLA–PEB–PLA triblock oligomers with the 2-ureido-4[1H]-pyrimidinone (UPy) self-complementary quadruple hydrogen bonding units. Such supramolecular copolymers (SMPs) exhibit the characteristic properties of thermoplastic elastomers. The thermal, morphological, mechanical, shape memory, and self-healing properties of SMPs can be readily modulated by varying the composition, stereostructure, and crystallizability of PLA blocks. The prepared SMPs are shown as transparent and elastic films, while their PLA–PEB–PLA precursors are viscous or brittle solids. Crystallization of isotactic PLA blocks, i.e. poly(L-lactic acid) (PLLA), in SMPs is significantly impeded by the end-caped UPy motifs. The prepared SMPs show a well-defined microphase-separated structure, which varies from cylindrical to lamellar morphology with the increasing fraction of PLA blocks. Compared to the PLA–PEB–PLA precursors, SMPs exhibit improved mechanical strengths, modulus, elongation-at-break, good thermally-induced shape memory and light-triggered self-healing properties. The recovery ratios of SMPs containing atactic poly(D,L-lactic acid) (PDLLA) blocks are nearly 100%. The shape memory and self-healing properties of SMPs can be modulated by the stereostructure of PLA segments and they become worse when the isotactic, crystallizable PLLA segments are presented.

Effect of comonomer-unit compositional distribution on thermal and crystallization behavior of bacterial poly[(3-hydroxybutyrate)-co-(3-mercaptopropionate)].

The physical properties of novel sulfur-containing biopolymers, poly[(3-hydroxybutyrate)-co-(3-mercaptopropionate)]s [P(3HB-co-3MP)s], have been investigated in detail by(1)H and (13)C NMR spectroscopy, wide-angle X-ray diffraction (WAXD) analysis, DSC, and FT-IR spectroscopy. Based on a solvent/non-solvent (chloroform/heptane) fractionation method, an original P(3HB-co-3MP) sample with 3MP unit content of 16.3 mol-% was fractionated into eight fractions with 3MP unit content ranging from 10.3 to 37.2 mol-% and number-average molecular weight from 0.4 x 10(5) to 2.9 x 10(5). The thermal and crystallization behavior were found to be greatly affected by the comonomer-unit composition and its distribution. Furthermore, the 3MP comonomer unit was found to be included in the crystalline phase in some fractions.

Gas Permeability and Permselectivity of Poly(L‐Lactic Acid)/SiOx Film and Its Application in Equilibrium‐Modified Atmosphere Packaging for Chilled Meat

A layer of SiOx was deposited on the surface of poly(L-lactic acid) (PLLA) film to fabricate a PLLA/SiOx layered film, by plasma-enhanced chemical vapor deposition (PECVD) process. PLLA/SiOx film showed Youngs modulus and tensile strength increased by 119.2% and 91.6%, respectively, over those of neat PLLA film. At 5 °C, the oxygen (O2 ) and carbon dioxide (CO2 ) permeability of PLLA/SiOx film decreased by 78.7% and 71.7%, respectively, and the CO2 /O2 permselectivity increased by 32.5%, compared to that of the neat PLLA film. When the PLLA/SiOx film was applied to the equilibrium-modified atmosphere packaging of chilled meat, the gas composition in packaging reached a dynamic equilibrium with 6% to 11% CO2 and 8% to 13% O2 . Combined with tea polyphenol pads, which effectively inhibited the microbial growth, the desirable color of meat was maintained and an extended shelf life of 52 d was achieved for the chilled meat.

Sulfated polysaccharide heparin used as carrier to load hydrophobic lappaconitine.

One-step self-assembly was used to prepare pH-sensitive lappaconitine-loaded low-molecular-weight heparin (LMWH-LA) and to demonstrate that the sulfur group promotes dissolution and has synergistic effect on the analgesic property of lappaconitine (LA). The LMWH-LA was characterized in terms of releasing behavior, pH-sensitivity, analgesic activity and anticoagulation property. The drug loading level of LA in low-molecular-weight heparin (LMWH) reached 24.3% (w/w). The LA, self-assembled in LMWH, released faster in an acidic environment than that in neutral or alkaline environments. Analgesic experiments showed that the LMWH-LA had earlier onset time and longer duration than the LA. Compared with LMWH, the LMWH-LA can reduce clotting time more effectively. These results suggest that the LMWH is a good template and has great potential to achieve synergistic effect of LA. In addition, similar macromolecular structure can be used as a new natural polymeric carrier for loading hydrophobic alkaloids.

Improved mechanical and barrier properties of PPC multilayer film through interlayer hydrogen bonding interaction

Poly(propylene carbonate) (PPC) is coated with cellophane (PT) via the intermolecular hydrogen bonds of chitosan (CS) with the both polymers, and their multilayer films are prepared in different weight ratios. The trace presence of chitosan on the surface of PT promotes the combination with PPC layers. After coating, the Young’s modulus and tensile strength of PPC are greatly improved, the storage modulus still keep a high value between ∼0–70°C. The oxygen barrier of PPC is increased at least 580 times, and the multilayer films still keep good water vapor barrier in some degree.

Studies on Comonomer Compositional Distribution of Poly(propylene carbonate-propylene oxide) Copolymer and Its Effect on the Thermal, Mechanical and Oxygen Barrier Properties of Fractions

Poly(propylene carbonate) (PPC) was synthesized by the alternating copolymerization of carbon dioxide and propylene oxide (PO). However, during the polymerization, two by-products tended to produce cyclic propylene carbonate (CPC) and a polyether (PE) segment. The excess PO repeat units (PE segment) can easily insert into the PPC backbone and eventually produce the PPC–PO copolymer. The production of CPC and PE segments affected the increase of polymer chain length. In order to investigate the effects of the existence of PE segments, CPC, and molecular weight of fractions on the physical properties of PPC–PO copolymer, a series of fractions with narrow molecular weight distribution were obtained by repeated fractionation. Based on a solvent/non-solvent (chloroform/n-heptane) mixture, an original PPC–PO sample was fractionated into nine fractions with number–average molecular weights (Mn) from 0.34 × 105 to 5.56 × 105 and PE content from 0.4 to 15 mol%. The Mn of PPC–PO fractions decreased with the increase of PE content in the PPC–PO backbone, and the thermal and mechanical properties of the PPC–PO copolymers were affected by their Mn and PE contents. Furthermore, the lower the PE content, the higher the Mn value. Higher Mn means better tensile and lower oxygen permeability of PPC–PO copolymer.

Hydrophobic lappaconitine loaded into iota-carrageenan by one step self-assembly

New data on the loading of pH-sensitive lappaconitine loaded into iota-carrageenan (LA-ICG) is provided. This LA-ICG ionic biopolymer was prepared by one step self-assembly. The LA-ICG was characterized in terms of the loading capacity, lappaconitine (LA) releasing behavior, pH-sensitivity, and analgesic properties. Iota-carrageenan (ICG) high loading capacity reached up to 26.18% (w/w). Also, the LA, loaded with ICG, was released faster in an acidic environment than that in neutral or alkaline environments. Animal analgesic experiments showed that the LA-ICG of low molecular weight had earlier onset time and longer duration than the LA. These results suggest that the ICG of low molecular weight has great potential to achieve the synergistic effect of LA. In addition, the ICG can be used as a novel natural polymeric carrier for loading a hydrophobic alkaloid.

Mechanical and Gas Barrier Properties of Poly(L-Lactic Acid) by Plasma-Enhanced Chemical Vapor Deposition of SiOx

ABSTRACT In this work, poly(L-lactic acid) film was coated with SiOx by the plasma-enhanced chemical vapor deposition with different deposition times. Compared with the neat poly(L-lactic acid) film, the oxygen (O2), carbon dioxide (CO2), nitrogen (N2), and water vapor permeability of the poly(L-lactic acid)/SiOx60 film (depositing for 60 min) decreased by 40.7, 30.6, 58.7, and 53.4% at 25°C, respectively. After treated by the SiOx deposition, the gas permselectivity of the poly(L-lactic acid)/SiOx60 film, such as α(CO2/O2), α(O2/N2), and α(CO2/N2), increased by 17.2, 43.9, and 67.5% at 25°C, respectively. In addition, Young’s modulus and tensile strength of poly(L-lactic acid)/SiOx60 film increased by 107.2 and 49.3%, respectively. Moreover, the poly(L-lactic acid)/SiOx60 films still kept good toughness with an elongation at break of 50.7%. GRAPHICAL ABSTRACT